1. Field of the Invention
The present invention relates to multifocal ophthalmic lenses to correct vision of an eye, such as multifocal intraocular lenses, multifocal contact lenses, and multifocal spectacles.
2. Description of Background Art
Presbyopia is a condition that affects the accommodation properties of the eye. As objects move closer to a young, properly functioning eye, the effects of ciliary muscle contraction and zonular relaxation allow the lens of the eye to change shape, and thus increase its optical power and ability to focus at near distances. This accommodation can allow the eye to focus and refocus between near and far objects.
Presbyopia normally develops as a person ages, and is associated with a natural progressive loss of accommodation. The presbyopic eye often loses the ability to rapidly and easily refocus on objects at varying distances. The effects of presbyopia usually become noticeable after the age of 45 years. By the age of 65 years, the crystalline lens has often lost almost all elastic properties and has only limited ability to change shape.
Along with reductions in accommodation of the eye, age may also induce clouding of the lens due to the formation of cataracts. Cataracts may form in the central nucleus of the lens, in the peripheral cortical portion of the lens, or at the back of the lens. Cataracts can be treated by the replacement of the cloudy natural lens with an artificial lens. An artificial lens replaces the natural lens in the eye, with the artificial lens often being referred to as an intraocular lens (hereinafter “IOL”).
A variety of prior technologies have been developed to enhance the ability of IOLs to facilitate viewing in presbyopic patients. For example, multifocal IOLs may rely on a diffractive optical surface to direct portions of the light energy toward differing focal distances, thereby allowing the presbyopic patient to see both near and far objects. Diffractive multifocal ophthalmic lenses have been proposed for treatments of presbyopia without removal of the natural crystalline lens, for example diffractive contact lenses.
A multifocal diffractive profile of the lens can be used to mitigate presbyopia by providing two or more optical powers, for example, one optical power for near vision and one optical power for far vision. These lenses may be in the form of a multifocal contact lens, for example a bifocal contact lens. The lenses may also take the form of an intraocular lens placed within the capsular bag of the eye, replacing the original lens.
Although multifocal diffractive ophthalmic lenses have improved the quality of vision for many presbyopic patients, additional improvements would still be beneficial. For example, at least some patients may experience unwanted light-related visual phenomenon (hereinafter “dysphotopsia”) in at least some instances, such as halos from out of focus objects or optical effects that may be related to light scatter, for example, which can contribute to dysphotopsia. Diffractive multifocal lenses may direct visually significant amounts of light energy at other non-viewing foci, which can contribute to the unwanted light-related visual phenomenon experienced by the patient. Although multifocal diffractive lenses can be designed and optimized for a particular wavelength, people see in color and vision quality and light scatter can change at visible wavelengths away from the design wavelength such that vision quality may be less than ideal in at least some instances. The human eye responds to wavelengths of light within the visible spectrum having a range from about from about 400 nm to about 800 nm, and polychromatic light, for example white light, encompasses several wavelengths of visible light energy having wavelengths within this range. Although diffractive optics may work quite well at a design wavelength, for example at about 550 nm, the eye remains sensitive to light a wavelengths away from the design wavelength such as at about 500 nm and 600 nm, such that visual phenomenon may be observed with light away from the design wavelength in at least some instances.
A diffractive multifocal lens may have a diffractive profile that corresponds to a fraction of the design wavelength in at least some instances, such that light diffracts to multiple orders to provide the multifocal effect and mitigate presbyopia substantially. However, the diffraction of light to two or more orders with a diffractive profile that is a fraction of the design wavelength can be somewhat indirect and can diffract light to other adjacent orders such that patient vision can be less than ideal in at least some instances. Also, the diffraction of light to two or more orders from the profile can be at least somewhat sensitive to wavelength such that the amount of light diffracted to near and far focus can vary with wavelength in at least some instances. The optical properties of diffractive lenses can change with wavelength and viewing angle such that in at least some instances objects away from the optical axis of the eye can increase light scatter that can vary with wavelength and contribute to dysphotopsia in at least some instances.
Depth perception can be an important aspect of vision, and at least some of the prior multifocal lens may provide less depth perception than would be ideal in at least some instances. Intermediate vision correction can be helpful for depth perception and at least some of the prior diffractive optical lenses can provide less than ideal intermediate vision correction in at least some instances. For example, although apodization of a diffractive profile providing near and far vision correction has been proposed to provide increased relative amounts of light for far vision correction at larger pupil sizes, this approach can leave intermediate vision substantially uncorrected and result in wavelength dependent light scatter such that depth perception can be less than ideal in at least some instances.
In light of the above, it would be beneficial to provide improved multifocal lenses that overcome at least some of the limitations of the prior lenses. Ideally such improved lenses would provide diffractive multifocal lenses having diffractive profiles that improve the distribution of light energy distribution between viewing and non-viewing foci, vary the amount of light energy for near and far vision correction in a controlled manner in response to variation in pupil size, provide intermediate vision correction, decrease chromatic aberration, and decrease light scatter with off axis viewing so as to improve the quality of vision.